Ceria zirconia alumina composition with enhanced thermal stability

ABSTRACT

The subject matter of the invention is a method for producing composites, comprising mixed oxides of aluminum oxide and cerium/zirconium, hereinafter referred to briefly as Al/Ce/Zr oxide composite(s), using boehmite and soluble cerium/zirconium salts. Al/Ce/Zr oxide composites produced in this way have an increased thermal stability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a division of U.S. patent application Ser. No.13/549,020, filed Jul. 13, 2012, which claims the benefit of EuropeanPatent Application No. EP 11193944.3, filed Dec. 16, 2011, and GermanPatent Application No. DE 102011107702.6, filed Jul. 14, 2011, thedisclosures of which are incorporated herein in their entirety.

BACKGROUND

The present invention refers to compositions based on ceria (oxide ofcerium), zirconia (oxide of zirconium) and alumina (oxide of aluminium)with enhanced thermal stability.

Such compositions may be used as washcoats in the application of exhaustgas aftertreatment of combustion engines such as fuel- and dieselengines, e.g. as components of catalysts (mainly Three Way Catalysts,TWC), but also in other parts integrated into the exhaust stream such asNOx traps, Diesel Oxidation Catalysts (DOC) and Diesel ParticulateFilters (DPF).

Ceria-Zirconia based mixed oxides and alumina are widely used inautomotive application for catalyst preparation. For example, in WO2008/113457 the preparation of washcoats introducing separately mixedoxides of ceria/zirconia and alumina (lanthanum doped aluminium oxide)is described and thus is a well established process.

However, there is also drawn attention to other types of compositionmaterials consisting of Al₂O₃ with the balance typically being CeO₂,ZrO₂, and optionally stabilizers such as rare earth metal oxides or nonrare earth metal oxides. For example, in U.S. Pat. No. 5,883,037 suchtypes of composition materials are described paying attention also tothe surface stability of such compounds. E.g. in column 1, line 32 to 35it is reported that surface stability of Ce—Zr-Alumina based materialsamongst other properties is important to be effective as a catalyst. Inmore detail, example 1 of U.S. Pat. No. 5,883,037 refers to acomposition of 50% Al₂O₃/La₂O₃ (97%/3%) and 50% CeO₂/ZrO₂/Pr₆O₁₁/Fe₂O₃(56%/30%/7%/7%). The composition oxide exhibits a specific surface areaof 52 m²/g after being heat treated at 600° C. for 2 hours and afteradditional heat treatment for 2 hours at 1050° C. No values on specificsurface area are reported for heat treatment at higher temperaturesand/or for a longer period of time.

In EP 1 172 139 there is reported the preparation and the thermalstability of several Al—Ce—Zr—Y—La composition oxides and variouscompositions consisting of Al₂O₃/CeO₂/ZrO₂/Y₂O₃ La₂O₃ with differentratios of the oxides are disclosed. The materials are described to beprepared via co-precipitation starting from the corresponding metal saltsolutions. As intermediates suspensions of Al—Ce—Zr—Y—La hydroxides areformed which after calcination were transferred into the correspondingoxides (see page 8, lines 1 to 6). The surface area of such compositionoxides is described to be dependent on the amount of Al₂O₃ being presentin the composition. In examples 10 to 22 in which the Al₂O₃ content isin the range between 21 and 25 weight % (calculated from the molarratios disclosed in table 2) the specific surface area is less than 15m²/g after the compounds have been subjected to heat treatment at 1100°C. for 20 hours (see table 2 page 14). Higher values of the surface areaare indicated after heat treatment at 1100° C./20 hours in case that theAl₂O₃ content is increased as disclosed in the examples 24, 27 and 31.More in detail, in example 24 corresponding to a composition with anAl₂O₃ content of 57% weight, there is disclosed a surface area of 27m²/g after calcination at 1100° C./20 hours, and in examples 27 and 31which correspond to an Al₂O₃ content of 63%, surface areas of 31 m²/gand 30 m²/g, respectively, after calcination at 1100° C./20 hours areindicated.

In WO 2006/070201 there is reported an improved method for the formationof composition hydroxides or oxides comprising, on an oxide basis,alumina (Al₂O₃) and Zirconia (ZrO₂), and optionally including at leastone member selected from CeO₂, La₂O₃, Nd₂O₃, Pr₆O₁₁, Sm₂O₃. Y₂O₃ andoptionally other rare earth metal oxides. The compounds are described tobe made by co-precipitation starting from a metal salt solution usingcaustic alkali as a precipitation agent. A strict narrow pH range is tobe kept: According to WO 2006/070201 the deviation of the pH duringprecipitation must not be more than +/−1. In example 6 in WO 2006/070201a Al/Ce/Zr-composition oxide is reported consisting of 51% Al₂O₃, 14.2%CeO₂ and 34.8% ZrO₂ exhibiting a surface area of 43 m²/g after beingheat treated at 850° C./4 hours and at 1100° C./2 hours. After moresevere ageing (heat treatment at 850° C./4 hours and 1200° C./2 hours)the compound exhibits a surface area of 16 m²/g only. No information onthe surface areas are disclosed for the case where the composition oxideis heat treated for a longer period of time, e.g. 850° C./4 hours+1150°C./36 hours. Beside the disadvantage of the drop in surface area afterlong ageing time moreover the process for manufacturing the compositionoxides as disclosed in WO 2006/070201 has some disadvantages. Namely,the precipitate formed by co-precipitation from the mixed metal-solution(Al, Ce, Zr) requires an extensive washing and re-slurrying for properremoval of the caustic alkali which was used for precipitating the metalcomposition. In addition, a hydrothermal treatment at 120° C. of thematerial obtained prior to final calcination of the hydroxides (wetcake) is described to be required to get material with reasonablestability in surface area. However, though the materials are describedto be re-slurried and subjected to extensive washing the final productsstill contains Na in a range of up to 100 ppm. Na is an undesiredimpurity in materials for automotive application since it might bedetrimental to the action of rhodium which for example is part of athree way catalyst for the removal of NOx (see e.g. Norman Macleod etal. in Applied Catalysis B: Environmental, Volume 33, Issue 4, Oct. 25,2001, Pages 335-343). In addition, the use of huge amounts of causticalkali in the precipitation step generates heavily contaminated nitratecontaining waste water causing environmental concerns.

In U.S. Pat. No. 6,831,036 contacting cerium and zirconium nitrates inaqueous solution with Boehmite is described.

In U.S. Pat. No. 6,306,794 the preparation of composite oxidesaluminiumoxide and cerium/zirconium oxides) and a binder is described.Hydroxides from cerium and zirconium are not indicated in U.S. Pat. No.6,306,794.

In WO 2006/119549 there is described the dissolution of nitrates ofcerium and zirconium.

Hydroxides of cerium and zirconium are not water soluble and are thusnot present in a salt solution of cerium/zirconium.

In spite of the fact that oxides of alumina and oxides of ceria/zirconiaas well as composition oxides of Al/Ce/Zr are already used worldwide inautomotive applications, there is still the need to improve productionroutes and the performance of such materials, especially in terms oftheir thermal stability to avoid a drop of surface area when exposingsuch materials to higher temperatures and to enhance the life time ofsuch catalysts.

SUMMARY

The present invention is aimed to solve disadvantages related with thelimited thermal stability of Al/Ce/Zr compositions and to improve themanufacturing process of such compounds/compositions; in particular toavoid co-precipitation with formation of huge amount of waste water andhydrothermal treatment steps and moreover, to provide compositions withenhanced surface stability, particularly after long term ageing.

DETAILED DESCRIPTION

In one aspect the present invention provides a process for thepreparation of a calcined mixed oxide comprising Al-, Ce- and Zr-oxides,comprising the steps of

-   -   (a) providing an aqueous slurry comprising hydroxides of cerium        and zirconium,    -   (b) contacting the hydroxides of cerium and zirconium with an        alumina precursor to obtain an aqueous suspension of solids,    -   (c) isolating the solids from the aqueous suspension and drying        to obtain a solid composition,    -   (d) calcining the solid composition of step (c) at a temperature        from 450° C. to 1200° C. for at least 1 hour to obtain a        calcined mixed oxide.

The Al/Ce/Zr-oxides according to the present invention preferably havesurface areas (BET) exceeding 20 m²/g or even 30 m²/g when treated for 4h at 1200° C.

A process provided by the present invention is herein also designated as“A process of (according to) the present invention.”

Preferably the aqueous slurry in step (a) comprises cerium calculated ascerium oxide (CeO₂) in the range of 5% to 90% by weight based on thetotal oxide content (TO) of the calcined mixed oxide.

Preferably the calcined mixed oxide in step (d) comprises cerium from 5%to 90% by weight, preferably 5% to 50% by weight, aluminium from 20% to80% by weight, preferably 40% to 70% by weight, zirconium from 5% to 80%by weight, preferably 5% to 40% by weight, and optionally rare earthmetals (RE) from 0% to 12% by weight, preferably 0.1% to 9% by weight;wherein cerium, zirconium, and rare earth metals (RE) are calculated asCeO₂, ZrO₂, Al₂O₃, or RE₂O₃, respectively.

In another aspect the present invention provides a process according tothe present invention, wherein the calcined mixed oxide comprises

-   -   cerium from 5% to 90% by weight, preferably 5% to 50% by weight,    -   aluminium from 20% to 80% by weight, preferably 40% to 70% by        weight,    -   zirconium from 5% to 80% by weight, preferably 5% to 40% by        weight, and optionally    -   0% to 12% by weight, preferably 0.1% to 9% by weight of rare        earth metals (RE);    -   wherein cerium, zirconium, and rare earth metals (RE) are        calculated as CeO₂, ZrO₂, Al₂O₃, or RE₂O₃, respectively.

An advantageous embodiment of a process of the present invention ischaracterized in that the Ce/Zr-hydroxides used according to step (a)contain at least one rare earth metal element, preferably selected fromY, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

In another aspect the present invention provides a process according tothe present invention, wherein the aqueous slurry in step (a) furthercomprises one or more hydroxides of rare earth metals other than cerium.

An aqueous slurry as defined in step (a) in a process of the presentinvention includes either an aqueous slurry 1, or an aqueous slurry 2.An aqueous slurry 1 is a suspension of hydroxides of cerium andzirconium, optionally comprising further rare earth metal salts whichwas treated with ammonium hydroxide, and optionally with H₂O₂ and/or asurfactant.

An aqueous slurry 2 is an aqueous slurry 1 isolated (e.g. filtrated) asa solid (Wet Cake) and re-suspended in water, optionally furthertreated, e.g. with ammonia and/or a surfactant.

Step (a) may be carried out by providing an aqueous solution of ceriumand zirconium salts, optionally in combination with other rare earthmetal salts and treating the aqueous solution with aqueous ammoniumhydroxide. Optionally and preferably a treatment with H₂O₂ is carriedout, either before ammonium hydroxide treatment, or after ammoniumhydroxide treatment. A pH of 7 and higher, e.g. 7 to 10 of the aqueousslurry is adjusted. A precipitate forms and aqueous slurry 1 isobtained. Aqueous slurry 1 may be used in a step (b) as such, or thesolid from aqueous slurry 1 may be isolated (Wet Cake), e.g. byfiltration and the isolated solid may be resuspended and further treatedwith ammonia. Optionally a treatment with a surfactant is carried out,either slurry 1 or slurry 2, or the isolated solid from slurry 1 may becontacted with a surfactant. Step (a) preferably is carried out attemperatures from 10° C. to 40° C., preferably at room temperature.

Step (b) may be carried out by mixing the aqueous slurry of step (a), orthe isolated solids from the aqueous slurry of step (a) with an aluminaprecursor, e.g. aluminium hydroxide, e.g. a Boehmite, in aqueoussuspension. Step (b) preferably is carried out at temperatures from 10°C. to 40° C., preferably at room temperature. An aqueous suspension ofsolids is obtained. Optionally a treatment with a surfactant is carriedout in step (b) by adding a surfactant to the aqueous suspension.Optionally the alumina precursor may be treated with a surfactant beforemixing with the aqueous suspension of step (a).

In step (c) the solids from the aqueous suspension are isolated, e.g. byfiltration, centrifugation, preferably filtration and are dried. Dryingpreferably is carried out at temperatures from 90° C. to 150° C.,optionally under vacuum. Optionally the solid composition is contacted,e.g. impregnated with a surfactant. A solid composition is obtainedwhich is subjected to step (d).

The solid composition obtained in step (c) is subjected to calcinationin step (d), i.e. heat treated at temperatures from 450° C. to 1200° C.,preferably 600° C. to 1000° C., e.g. 800° C. to 900° C., for at least 1hour, e.g. for several hours, e.g. 1 hour to 10 hours, such as 2 hoursto 6 hours.

According to the present invention it was surprisingly found that theuse of a surfactant in a process of the present invention may influence,e.g. may increase the stability of the surface area of the finalAl/Ce/Zr composition.

If a surfactant is used in a process according to the present invention,preferably either the starting mixture of step (a) comprises asurfactant, e.g. a surfactant is added in step (a), or a surfactant isadded in step (b); or a surfactant is added in step (d).

In another aspect the present invention provides a process according tothe present invention comprising using a surfactant; e.g. the aqueousslurry of step (a) comprises a surfactant, e.g. a surfactant is added instep (a); and/or the aqueous suspension of solids in step (b) comprisesa surfactant, e.g. a surfactant is added in step (b); and/or the solidcomposition in step (d) comprising a surfactant, e.g. a surfactant isadded to the solid composition in step (d).

In one embodiment of the present invention in a process of the presentinvention the aqueous slurry in step (a) and/or the aqueous suspensionof solids in step (b) comprises a surfactant, e.g. wherein thesurfactant is added before the solid component is added.

Appropriate surfactants for use in a process of the present inventioninclude compounds which lower the interfacial tension of a liquid and asolid, e.g. including organic compounds, e.g. such which are amphiphilicand contain both hydrophobic groups and hydrophilic groups. Preferredsurfactants include nonionic surfactants, e.g. nonionic surfactantscomprising ethylene oxide/propylene oxide units, such as Triton®,Tergitol®, e.g. including ethyl phenol ethoxylates and ethyleneoxide/propylene oxide copolymers, or lauric acid.

In another aspect the present invention provides a process according tothe present invention, wherein the drying in step (c) comprises i)filtration and air drying, e.g. drying at elevated temperatures and/or,ii) spray drying.

It was also surprisingly found that the enhanced stability of surfacearea of the Al/Ce/Zr compositions may be influenced by the chemicalnature of the alumina precursor used. Interesting results are obtained,if the alumina precursor in step (b) comprises Boehmite of formula(AlO(OH)xH₂O) and optionally aluminium hydroxide, optionally the aluminaprecursor in step (b) consists of Boehmite.

A preferred Boehmite in a process of the present invention has porevolumes of 0.4 to 1.2 ml/g and/or crystallite sizes of 4 nm to 40 nm,preferably 4 nm to 16 nm, measured at the (120) reflection.

Independent thereof a Boehmite in a process of the present inventionpreferably has a purity as follows: Contents of

-   -   Si approximately 0.01% or lower, calculated as SiO₂;    -   Fe₂O₃ approximately 0.01% or lower calculated as Fe₂O₃;    -   Na approximately 0.002% or lower, calculated as Na₂O;    -   K approximately 0.002% or lower, calculated as K₂O;    -   Ti approximately 0.005% or lower, calculated as TiO₂,    -   other elements approximately 0.01% or lower, calculated as their        oxides.

A Boehmite according to the present invention is a compound of formulaAlO(OH) x H₂O. Preferred is a Boehmite obtainable by hydrolysis ofaluminium alcoholate, e.g. obtainable via a process as disclosed in U.S.Pat. No. 5,055,019 (“Process for the Production of Boehmitic Aluminas”).According to this process boehmitic alumina with a purity of at least99.95% Al₂O₃ is obtained having defined pore radii in the range of 3 nmto 100 nm by salt-free hydrolysis of aluminium alcoholates in water,whereby the Boehmite slurry obtained is aged in a autoclave at a watervapour pressure of 1 bar to 30 bar corresponding to a temperature of100° C. to 235° C. over a period of time of 0.5 hour to 20 hours and bystirring with a circumferential speed of 1.0 m/s to 6.0 m/s.

According to a preferred embodiment of the present invention aluminiumalcoholates are used as starting material to obtain a Boehmite of highpurity. The aluminium alcoholates can be produced by the so calledZiegler-Process preferably comprising a filtration step as a cleaningstep. C₁- to C₂₄-alcohols, or mixtures thereof may be used to form thealuminium alcoholates.

According to another preferred embodiment a Boehmite or Boehmite slurryused comprise lanthanum or barium compounds, preferably such which aresoluble in water under the reaction conditions, in order to obtain aBoehmite, comprising 1% to 10% by weight of lanthanum and/or barium,calculated as La₂O₃ or BaO, respectively,

The process of the present invention is useful for the preparation of acatalyst composition with outstanding favorable and surprisingproperties as described herein.

In comparative example 1 of the present application it is shown that, incase that the co-precipitation process as disclosed in EP 1 172 139 isapplied to a composition being different from the compositions disclosedtherein, a material with significant lower surface stability incomparison with a composition prepared according to the presentinvention is obtained. On preparing a composition consisting of 50%Al₂O₃, 10% CeO₂, 36.5% ZrO₂, 1% La₂O₃ and 2.5% Nd₂O₃ according to theprocess disclosed in EP 1 172 139 a surface area of 31 m²/g is obtainedafter ageing of the material at 1100° C./20 hours. In contrast to that,if a process according to the present invention is used for thepreparation of the identical composition, significant higher surfaceareas after ageing at 1100° C./20 hours, namely in a range from 40 m²/gto 50 m²/g are obtained, e.g. as lined out in examples 4 to 9 and 16 to19 of the present application.

For the purpose of investigating the surface stability at more severeageing conditions (higher temperatures and longer ageing time)comparative example 2 is provided in the present application. It isshown that a composition consisting exactly of the same components asreferred to in example 1 and prepared according to example 1 of U.S.Pat. No. 5,883,037 by contacting a lanthanum doped alumina with aprecipitate generated by ammonia out of a mixed metal salt solutionbased on ceria/zirconia/praseodymium and iron, exhibits a surface areaof 27 m²/g after calcination at 1100° C./4 hours, but only 5 m²/g aftercalcination at 1150° C./36 hours and 7 m²/g after calcination at 1200°C./4 hours.

To investigate the properties of heat stability after ageing for alonger period of time a compound was synthesized as disclosed incomparative example 3 of the present application according to the methodof example 6 of WO 2006/070201. The surface area values found for theafter heat treatment at 850° C./4 hours and 1050° C./36 hours and afterheat treatment at 850° C./4 hours and 1150° C./36 hours were 50 m²/g(850° C.) and 19 m²/g (1050° C./1150° C.), respectively.

Thus, in a further aspect the present invention provides a composition,e.g. a catalyst composition obtainable, e.g. obtained, according to aprocess of the present invention.

A calcined mixed oxide obtainable, e.g. obtained, according to a processof the present invention preferably is a composite material comprisingaluminium oxide and a solid solution of cerium oxide and zirconiumoxide, optionally further comprising rare earth metal oxides.

According to the present invention it was found that a Boehmite mayimprove the stability of surface area of Al/Ce/Zr-oxide compositions.

In a further aspect the present invention provides the use of a Boehmitefor improving the stability of surface area of Al/Ce/Zr-oxidecompositions.

A solid solution of cerium oxide and zirconium oxide, optionally furthercomprising rare earth metal oxides may be obtained as appropriate, e.g.according, e.g. analogously, to a known process.

In the following examples all temperatures are in degree Celsius (° C.)and are uncorrected.

The following abbreviations are used in the description and examplesherein:

-   -   BET BET theory aims to explain the physical adsorption of gas        molecules on a solid surface and serves as the basis for an        important analysis technique for the measurement of the specific        surface area of a material. In 1938, Stephen Brunauer, Paul Hugh        Emmett, and Edward Teller published an article about the BET        theory in for the first time in J. Am. Chem. Soc., 1938, 60, 309        (Internet doi:10.1021/ja01269a023). “BET” consists of the first        initials of their family names.    -   ROI Residue on Ignition at 1000° C./2 hours    -   rt room temperature    -   TO Total Oxide

The percent indication of the oxides as indicated herein are indicationsin “% by weight.” Surface area (BET) analysis was performed withQuantachrome NOVA 4000 according to DIN (Deutsche Industrie Norm) 66131under use of N₂.

An aqueous slurry as referred to herein is either an aqueous slurry 1,or an aqueous slurry 2.

An aqueous slurry 1 is a suspension of hydroxides of cerium andzirconium, optionally comprising further rare earth metal salts whichwas treated with ammonium hydroxide, and optionally with H₂O₂ and/or asurfactant.

An aqueous slurry 2 is an aqueous slurry 1 isolated as a solid (WetCake) and re-suspended in water, optionally further treated, e.g. withammonia and/or a surfactant.

Preparation of Raw Materials Example A

Preparation of Ce/Zr/Rare Earth Hydroxide Suspension (Aqueous Slurry,Designated as “Wet Cake A” “Wet Cake B” and “Wet Cake C” afterFiltration)

Example A1

Wet Cake A: CeO₂(29%) ZrO₂(62%) La₂O₃ (9%)/TO

117.97 kg of an aqueous solution of cerium nitrate (CeO₂ content=29.5%),555.22 kg of an aqueous solution of zirconium nitrate (ZrO₂content=13.4%) and 29.03 kg of lanthanum nitrate in the form of crystals(La₂O₃ content=37.2%) were mixed with 497.78 kg of deionised water. Themixture obtained was stirred for 30 minutes and a clear solution wasobtained. To the solution obtained 18% aqueous ammonium hydroxide wereadded under virgourous stirring. A pH=3 was adjusted and to the mixtureobtained 52.9 kg of aqueous H₂O₂ (30%) were added simultaneously withammonia until a pH=7.25 was adjusted. The mixture obtained was stirredfor another half an hour. A precipitate formed and an aqueous slurry 1was obtained. The aqueous slurry 1 obtained was filtered via afilterpress. CeO₂(29%) ZrO₂(62%) La₂O₃(9%)/TO was obtained in the formof a solid and was washed with deionised water to obtain Wet Cake A:CeO₂(29%) ZrO₂(62%) La₂O₃(9%)/TO.

-   -   Yield=approximately 500 kg of Wet Cake A corresponding to 120 kg        of TO.    -   ROI=24.2%

Example A2

Wet Cake B: CeO₂(20%) ZrO₂(73%) La₂O₃(2%) Nd₂O₃(5%)/TO

346.6 g of an aqueous solution of cerium nitrate (CeO₂ content=28.9%),1503.9 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.27%), 26.53 g of lanthanum nitrate in the form of crystals(La₂O₃ content=37.7%) and 65.45 g of neodymium nitrate in the form ofcrystals (Nd₂O₃ content=38.2%) were treated with 2026 mL of deionisedwater and the mixture obtained was stirred for a few minutes and a clearsolution was obtained. To the solution obtained 994.6 mL of cooled (10°C.) aqueous 35% H₂O₂ were added and the mixture obtained was stirred forapproximately 45 minutes. To the mixture obtained an aqueous 24% ammoniasolution (cooled to 10° C.) was added dropwise with a dropping rate ofapproximately 40 mL/minute until a pH=9.5 was adjusted. A precipitateformed and and an aqueous slurry 1 was obtained. The aqueous slurry 1obtained was filtered. CeO₂(20%) ZrO₂(73%) La₂O₃(2%) Nd₂O₃(5%)/TO wasobtained in the form of a solid and was thoroughly washed with deionisedwater to obtain Wet Cake B: CeO₂(20%) ZrO₂(73%) La₂O₃(2%) Nd₂O₃(5%)/TO.

-   -   Yield=approx. 2750 g of Wet Cake B corresponding to 495 g of TO    -   ROI=18%

Example A3

Wet Cake C: CeO₂(56.3%) ZrO₂(40.4%) La₂O₃(1.2%) Y₂O₃(1.05%)/TO

971.5 g of an aqueous solution of cerium nitrate (CeO₂ content=28.9%),947.5 g of an aqueous solution of zirconium nitrate (ZrO₂content=21.33%), 15.53 g of lanthanum nitrate in the form of crystals(La₂O₃ content=37.7%) and 35.2 g of yttrium nitrate in the form ofcrystals (Y₂O₃ content=29.8%) were mixed with 2000 mL of deionised waterand the mixture obtained was stirred for a few minutes and a clearsolution was obtained. To the solution obtained 902 mL of cooled (10°C.) aqueous 35% H₂O₂ were added and the mixture obtained was stirred forapproximately 45 minutes. To the mixture obtained an aqueous 24% ammoniasolution (cooled to 10° C.) was added dropwise with a dropping rate ofapproximately 40 mL/minute until a pH=9.5 was adjusted. A precipitateformed and an aqueous slurry 1 was obtained. The aqueous slurry 1obtained was filtered. The solid obtained was thoroughly washed withdeionised water to obtain Wet Cake C: CeO₂(56.3%) ZrO₂(40.4%)La₂O₃(1.2%) Y₂O₃(1.05%)/TO.

-   -   Yield=approx. 2212 g of Wet Cake C, corresponding to 500 g of TO    -   ROI=22.6%

Example B

Preparation of Boehmite Powder and Boehmite Suspension

Example B1

Preparation of (Commercially Available) Boehmite DISPERAL HP 14

An alumina suspension or slurry resulting from neutral aluminiumalkoxide hydrolysis was prepared in the following manner: An aluminiumalkoxide mixture, such as obtained as an intermediate during thesynthesis of the Ziegler/Alfol process, was hydrolyzed at 90° C. in astirring vessel with deionized water. Two immiscible phases wereobtained, i.e. an upper alcohol phase and a lower alumina/water phase.The alumina/water phase contained Boehmite with an Al₂O₃ content of10-11%. 500 g of this alumina/water phase (pH 9) were separated andadded to a reactor in batch wise operation, at ambient reactor pressureand at 98° C. After setting the reactor conditions, ageing took placefor 16 hours using a conventional stirrer with a peripheral speed of 1.6m/s corresponding to a stirring rate of 500 rpm. The crystallite size ofthe spray dried material, measured at the (120) reflection was 13.5 nm.DISPERAL HP 14 was obtained.

Preparation of Aluminium-Hydroxide Suspensions

Boehmite Suspension Type 1

20.10 g of commercially available DISPERAL HP 14 (Al₂O₃ content 79.6%)were added to 379.9 g of water and stirred externally for 10 minutes.

Example B2

Preparation of (Commercially Available) Boehmite PURAL SB

An alumina suspension or slurry resulting from neutral aluminiumalkoxide hydrolysis was prepared in the following manner: An aluminiumalkoxide mixture, such as obtained as an intermediate during thesynthesis of the Ziegler/Alfol process, was hydrolyzed at 90° C. in astirring vessel with deionized water. Two immiscible phases wereobtained, i.e. an upper alcohol phase and a lower alumina/water phase.The alumina/water phase contained Boehmite and the alumina/water phasewas separated. The crystallite size of the spray dried material,measured at the (120) reflection, 2 was 5.0 nm. PURAL SB was obtained.

Preparation of Aluminium-Hydroxide Suspensions

Boehmite Suspension Type 2

24.0 g of commercially available PURAL SB (Al₂O₃ content 75.1%) wereadded to 376 g of water and stirred externally for 10 minutes.

Example B3

Preparation of Aluminium-Hydroxide Suspensions

Boehmite Suspension Type 3 (La-doped)

17.9 g of commercially available DISPERAL HP 14 (Al₂O₃ content 79.6%)were added to 382.1 g of water and stirred externally for 10 minutes.9.6 g of a La-acetate solution (La₂O₃ content 7.01%) were added to thissuspension and the resulting mixture was stirred for 30 minutes.

Example B4

Preparation of Aluminium-Hydroxide Suspensions

Boehmite Suspension Type 4 (La-doped)

23.25 g of commercially available DISPERAL HP 8 (Al₂O₃ content 77.4%)were added to 376.75 g of water and stirred externally for 10 minutes.10.8 g of a La-acetate solution (La₂O₃ content 7.01%) were added to thissuspension and the resulting mixture was stirred for 30 minutes.

Preparation of Al-, Ce- and Zr-oxides According to the Present Invention

Example 1

CeO₂(14.5%) ZrO₂(31%) La₂O₃(4.5%) Al₂O₃(50%)/TO

103.31 g of Wet Cake A, obtained according to Example A1, were suspendedin 200 mL of deionised water and the mixture obtained was stirred usingan external stirrer (Ultraturax) for 15 minutes. The pH of the mixtureobtained was adjusted to 9.5 using 24% aqueous ammonia solution and themixture obtained was stirred for a further 30 minutes. The aqueousslurry 2 obtained was filtered and the solid obtained was impregnatedwith 35.53 g of Triton X-100®. The impregnated solid obtained was addedto 555.56 g of Boehmite Suspension Type 1 (Al₂O₃ content=4.5%). Theaqueous suspension obtained was stirred vigorously using an externalstirrer for 30 minutes, was filtered and the solid obtained was dried at120° C. overnight. The solid composition obtained was calcined at 850°C./4 hours. Approximately 50 g of CeO₂(14.5%) ZrO₂(31%) La₂O₃(4.5%)Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 76 m²/g    -   BET after 1000° C./4 hours: 56.4 m²/g    -   BET after 1100° C./2 hours: 49.3 m²/g    -   BET after 1100° C./20 hours: 45.1 m²/g

Example 2

CeO₂(14.5%) ZrO₂(31%) La₂O₃(4.5%) Al₂O₃(50%)/TO

103.31 g of Wet Cake A, obtained according to Example A1, was suspendedin 200 mL of deionised water and the mixture obtained was stirred usingan external stirrer (Ultraturax) for 15 minutes. The pH of the mixtureobtained was adjusted to 9.5 using 24% ammonia solution and the mixtureobtained was stirred for a further 30 minutes. To the mixture obtained20.29 g of lauric acid were added and the mixture obtained was stirredfor another 30 minutes. The aqueous slurry 2 obtained was added to555.56 g of Boehmite Suspension Type 1 (Al₂O₃ content=4.5%). The aqueoussuspension obtained was stirred vigorously using an external stirrer for30 minutes, filtered and the solid obtained was dried at 120° C.overnight. The solid composition obtained was calcined at 850° C./4hours. Approximately 50 g of CeO₂(14.5%) ZrO₂(31%) La₂O₃(4.5%)Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 91 m²/g    -   BET after 1000° C./4 hours: 62 m²/g    -   BET after 1100° C./2 hours: 54 m²/g    -   BET after 1100° C./20 hours: 47 m²/g

Example 3

CeO₂(14.5%) ZrO₂(31%) La₂O₃(4.5%) Al₂O₃(50%)/TO

63.92 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.25%), 25.44 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%) and 5.97 g of lanthanum nitrate in the form of crystals(La₂O₃ content=37.7%) were treated with 230 mL of deionised water, themixture obtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 48.15 mL of cooled (10° C.) aqueous35% H₂O₂ were added and the mixture obtained was stirred forapproximately 45 minutes. To the mixture obtained an aqueous 24% ammoniasolution (cooled to 10° C.) was added dropwise with a dropping rate of40 mL/minute until a pH value of 9.5 was adjusted. The aqueous slurry 1obtained was added to 555.56 g of Boehmite Suspension Type 1 (Al₂O₃content=4.5%) and the aqueous suspension obtained was vigorously stirredusing an external stirrer. To the mixture obtained 15.9 g of TritonX-100® were added, the suspension obtained was stirred for another 30minutes and filtered. The solid obtained was dried at 120° C. overnightto obtain a solid composition which was calcined at 850° C./4 hours. 50g of CeO₂(14.5%) ZrO₂(31%) La₂O₃(4.5%) Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 87 m²/g    -   BET after 1000° C./4 hours: 77 m²/g    -   BET after 1100° C./2 hours: 59 m²/g    -   BET after 1100° C./20 hours: 47 m²/g

Example 4

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%)/TO

123.73 g of an aqueous solution of zirconium nitrate (ZrO₂content=29.5%), 35.09 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%) 2.65 g of lanthanum nitrate in the form of crystals(La₂O₃ 37.7%) and 6.54 g of neodymium nitrate in the form of crystals(Nd₂O₃ 38.2%) were treated with 475 mL of deionised water, the mixtureobtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 95.5 mL of cooled (10° C.) aqueous 35%H₂O₂ were added and the mixture obtained was stirred for approximately45 minutes. To the mixture obtained an aqueous 24% ammonia solution(cooled to 10° C.) was added dropwise with a dropping rate of 40mL/minute until a pH=9.5 was adjusted. A precipitate formed and theaqueous slurry 1 obtained was filtered. A solid was obtained, was washedwith deionised water and was impregnated with 32.8 g of Triton X-100 bywashing the precipitate with 15% solution of Triton X-100® in deionisedwater. The impregnated solid obtained was suspended in deionised waterand the aqueous slurry 2 obtained was mixed with 1111.1 g of BoehmiteSuspension Type 1 (Al₂O₃ content=4.5%). The aqueous suspension obtainedwas vigorously stirred using an external stirrer for 2 hours, filtered,and the solid obtained was dried at 120° C. overnight (approximately 20hours). The solid composition obtained was calcined at 850° C./4 hours.100 g of CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%) wereobtained.

-   -   BET after 850° C./4 hours (Fresh material): 99 m²/g    -   BET after 1000° C./4 hours: 87 m²/g    -   BET after 1100° C./2 hours: 65 m²/g    -   BET after 1100° C./20 hours: 53 m²/g

Example 5

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%)/TO

75.2 g of an aqueous solution of zirconium nitrate (ZrO₂ content=24.3%),35.09 g of an aqueous solution of cerium nitrate (CeO₂ content=28.5%)2.65 g of lanthanum nitrate in the form of crystals (La₂O₃ 37.7%) and6.54 g of neodymium nitrate in the form of crystals (Nd₂O₃ 38.%) weretreated with 475 mL of deionised water, the mixture obtained was stirredfor a few minutes and a clear solution was obtained. To the mixtureobtained 95.5 mL of cooled (10° C.) aqueous 35% H₂O₂ were added and themixture obtained was stirred for approximately 45 minutes. To themixture obtained an aqueous 24% ammonia solution (cooled to 10° C.) wasadded dropwise with a dropping rate of 40 mL/minute until a pH=9.5 wasadjusted. A precipitate formed and the aqueous slurry 1 obtained wasfiltered. The solid obtained was washed with deionised water and wasimpregnated with 15 g of Tergitol 15-S-9®. The impregnated solidobtained was suspended in deionised water and the aqueous slurry 2obtained was mixed with 555.56 g of Boehmite Suspension Type 1 (Al₂O₃content=4.5%). The aqueous suspension obtained was vigorously stirredusing an external stirrer for 2 hours and was filtered. The solidobtained was dried at 120° C. overnight (approximately 20 hours). Thesolid composition obtained was calcined at 850° C./4 hours to obtain 50g of CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%).

-   -   BET after 850° C./4 hours (Fresh material): 92.5 m²/g    -   BET after 1000° C./4 hours: 71 m²/g    -   BET after 1100° C./2 hours: 57 m²/g    -   BET after 1100° C./20 hours: 51 m²/g

Example 6

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%)/TO

150.52 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.25%), 35.09 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%) 2.65 g of lanthanum nitrate in the form of crystals(La₂O₃ 37.7%) and 6.54 g of neodymium nitrate in the form of crystals(Nd₂O₃ 38.2%) were treated with 574 mL of deionised water, the mixtureobtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 95.5 mL of cooled (10° C.) 35% H₂O₂were added and the mixture obtained was stirred for approximately 45minutes. To the mixture obtained an aqueous 24% ammonia solution (cooledto 10° C.) was added dropwise with a dropping rate of 40 mL/minute untila pH=9.5 was adjusted. To the mixture obtained 18.8 g of lauric acidwere added and the mixture obtained was stirred for 1 hour. Aprecipitate formed and the aqueous slurry 1 obtained was filtered. Thesolid thus obtained was washed with deionised water, suspended indeionised water and mixed with 1111.11 g of Boehmite Suspension Type 1(Al₂O₃ content=4.5%). The aqueous suspension obtained was vigorouslystirred using an external stirrer for 2 hours and filtered. The solidobtained was dried at 120° C. overnight. The solid composition obtainedwas calcined at 850° C./4 hours. 100 g of CeO₂(10%) ZrO₂(36.5%)La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 110 m²/g    -   BET after 1000° C./4 hours: 90 m²/g    -   BET after 1100° C./2 hours: 64 m²/g    -   BET after 1100° C./20 hours: 53 m²/g

Example 7

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%)/TO

139.66 g of Wet Cake B, obtained according to Example A2 (ROI 18%) weresuspended in 200 mL of deionised water, the aqueous slurry 2 obtainedwas stirred using an external stirrer (Ultraturex) for 10 minutes andwas mixed with 543.5 g of Boehemite Suspension Type 1 (Al₂O₃ content4.6%). The aqueous suspension obtained was stirred for 2 hours at rt andfiltered. The solid obtained was dried at 120° C. overnight and thesolid composition obtained was calcined at 850° C./4 hours.Approximately 50 g of CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%)Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 96 m²/g    -   BET after 1000° C./4 hours: 64 m²/g    -   BET after 1100° C./4 hours: 53 m²/g    -   BET after 1100° C./20 hours: 42 m²/g

Example 8

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%)/TO

146.1 g of Wet Cake B, obtained according to Example A2 (ROI 18%) weresuspended in 300 mL of deionised water, the mixture obtained was stirredusing an external stirrer (Ultraturex) for 10 minutes and 16.6 g ofTriton X-100® were added. The aqueous slurry 2 obtained was stirred for2 hours, mixed with 610 g of Boehmite Suspension Type 1 (Al₂O₃ content4.1%) and stirred for 2 hours. The aqueous suspension obtained wasspray-dried (inlet temperature: 220° C., outlet-temperature: 110° C.).The solid composition obtained was calcined at 850° C./4 hours.Approximately 50 g of CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%)Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 83 m²/g    -   BET after 1000° C./4 hours: 66 m²/g    -   BET after 1100° C./4 hours: 52 m²/g    -   BET after 1100° C./24 hours: 47 m²/g

Example 9

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%)/TO

136.1 g of Wet Cake B, obtained according to Example A2 (ROI 17.4%) weresuspended in 300 mL of deionised water, the aqueous slurry 2 obtainedwas stirred using an external stirrer (Ultraturex) for 10 minutes andthe mixture obtained was mixed with 610 g of Boehemite Suspension Type 1(Al₂O₃ content 4.1%). The aqueous suspension obtained was stirred for 2hours at rt and was spray-dried (inlet temperature: 220° C.,outlet-temperature: 110° C.). The solid composition obtained wascalcined at 850° C./4 hours. Approximately 50 g of CeO₂(10%) ZrO₂(36.5%)La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 63 m²/g    -   BET after 1000° C./4 hours: 60 m²/g    -   BET after 1100° C./4 hours: 50 m²/g    -   BET after 1100° C./24 hours: 44 m²/g

Example 10

CeO₂(13%) ZrO₂(47.5%) La₂O₃(1.3%) Nd₂O₃(3.25%) Al₂O₃(35%)/TO

195.67 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.25%), 45.61 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%), 3.45 g of lanthanum nitrate in crystal form (La₂O₃content=37.7%) and 8.51 g of neodymium nitrate in crystal form (Nd₂O₃content=38.2%) were treated with 574 mL of deionised water, the mixtureobtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 129.3 mL of cooled (10° C.) aqueous35% H₂O₂ were added and the mixture obtained was stirred forapproximately 45 minutes. To the mixture obtained an aqueous 24% ammoniasolution (cooled to 10° C.) was added dropwise with a dropping rate of40 mL/minute until the pH was adjusted to 9.5. To the mixture obtained24.4 g of lauric acid were added, the aqueous slurry 1 obtained wasstirred for 1 hour, filtered and the solid obtained was washed withdeionised water. The solid obtained was suspended in deionised water andthe aqueous slurry 2 thus obtained was mixed with 1111.11 g of BoehmiteSuspension Type 1 (Al₂O₃ content=4.5%). The mixture obtained wasvigorously stirred using an external stirrer for 2 hours, filtered, andthe solid obtained was dried at 120° C. overnight and calcined at 850°C./4 hours. 100 g of CeO₂(13%) ZrO₂(47.5%) La₂O₃(1.3%) Nd₂O₃(3.25%)Al₂O₃(35%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 84 m²/g    -   BET after 1000° C./4 hours: 73 m²/g    -   BET after 1100° C./2 hours: 49 m²/g    -   BET after 1100° C./20 hours: 42 m²/g

Example 11

CeO₂(7%) ZrO₂(25.55%) La₂O₃(0.7%) Nd₂O₃(1.75%) Al₂O₃(65%)

86.61 g of an aqueous solution of zirconium nitrate (ZrO₂content=29.5%), 24.56 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%) 1.86 g of lanthanum nitrate in the form of crystals(La₂O₃ 37.7%) and 4.58 g of neodymium nitrate in the form of crystals(Nd₂O₃ 38.2%) were treated with 200 mL of deionised water, the mixtureobtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 66.85 mL of cooled (10° C.) aqueous35% H₂O₂ were added and the mixture obtained was stirred forapproximately 45 minutes. To the mixture obtained an aqueous 24% ammoniasolution (cooled to 10° C.) was added dropwise with a dropping rate of40 mL/minute until a pH=9.5 was adjusted. A precipitate formed and theaqueous slurry 1 obtained was filtered. The solid obtained was washedwith deionised water and was impregnated with 23.01 g of Triton X-100®by washing the precipitate with an aqueous 15% solution of Triton X-100®in deionised water. The impregnated solid obtained was suspended indeionised water and the aqueous slurry 2 obtained was mixed with 1444.4g of Boehmite Suspension Type 1 (Al₂O₃ content=4.5%). The aqueoussuspension obtained was vigorously stirred using an external stirrer for2 hours and filtered. The solid obtained was dried at 120° C. overnight(approx. 20 hours) and the solid composition obtained was calcined at850° C./4 hours. 100 g of CeO₂(7%) ZrO₂(25.55%) La₂O₃(0.7%) Nd₂O₃(1.75%)Al₂O₃(65%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 106 m²/g    -   BET after 1000° C./4 hours: 99 m²/g    -   BET after 1100° C./2 hours: 76 m²/g    -   BET after 1100° C./20 hours: 65 m²/g

Example 12

CeO₂(7%) ZrO₂(25.55%) La₂O₃(0.7%) Nd₂O₃(1.75%) Al₂O₃(65%)

105.36 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.25%), 24.56 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%), 1.68 g of lanthanum nitrate in crystal form (La₂O₃content=37.7%) and 4.58 g of neodymium nitrate in crystal form (Nd₂O₃content=38.2%) were treated with 200 mL of deionised water, the mixtureobtained was stirred for a few minutes and the solution became clear. Tothe mixture obtained 66.8 mL of cooled (10° C.) aqueous 35% H₂O₂ wereadded and the mixture obtained was stirred for approximately 45 minutes.To the mixture obtained an aqueous 24% ammonia solution (cooled to 10°C.) was added dropwise with a dropping rate of 40 mL/minute until the pHwas adjusted to 9.5. To the suspension obtained 13.14 g of lauric acidwere added, the aqueous slurry 1 obtained was stirred for 1 hour,filtered and the Wet Cake 12/I obtained was washed with deionised water.Wet Cake 12/I obtained was suspended in deionised water to give anaqueous slurry 2 which was mixed with 1111.11 g of Boehmite SuspensionType 1 (Al₂O₃ content=4.5%). The aqueous suspension obtained wasvigorously stirred using an external stirrer for 2 hours and wasfiltered. The solid obtained was dried at 120° C. overnight and thesolid composition obtained was calcined at 850° C./4 hours. 100 g ofCeO₂(7%) ZrO₂(25.55%) La₂O₃(0.7%) Nd₂O₃(1.75%) Al₂O₃(65%) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 99 m²/g    -   BET after 1000° C./4 hours: 88 m²/g    -   BET after 1100° C./2 hours: 74 m²/g    -   BET after 1100° C./20 hours: 63 m²/g

Example 13

CeO₂(24.1%) ZrO₂(17.3%) La₂O₃(0.5%) Y₂O₃(0.9%) Al₂O₃(57.2)

71.34 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.25%), 84.56 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%), 1.33 g of lanthanum nitrate in crystal form (La₂O₃content=37.7%) and 2.94 g of yttrium nitrate in crystal form (Y₂O₃content=38.2%) were dissolved in 300 mL of deionised water, the mixtureobtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 75.1 ml of cooled (10° C.) aqueous 35%H₂O₂ were added and the mixture obtained was stirred for approximately45 minutes. To the mixture obtained an aqueous 24% ammonia solution(cooled to 10° C.) was added dropwise with a dropping rate of 40mL/minute until a pH=9.5 was adjusted. The aqueous slurry 1 obtained wasfiltered, the solid obtained was washed with deionised water and wasimpregnated with 25.5 g Triton X-100®. The impregnated solid obtainedwas suspended in deionised water and the aqueous slurry 2 obtained wasmixed with 1271.11 g of Boehmite Suspension Type 1 (Al₂O₃ content=4.5%).The aqueous suspension obtained was vigorously stirred using an externalstirrer for 2 hours and filtered. The solid obtained was dried at 120°C. overnight and the solid composition obtained was calcined at 850°C./4 hours. 100 g of CeO₂(24.1%) ZrO₂(17.3%) La₂O₃(0.5%) Y₂O₃(0.9%)Al₂O₃(57.2) were obtained.

-   -   BET after 850° C./4 hours (Fresh material): 94 m²/g    -   BET after 1000° C./4 hours: 82 m²/g    -   BET after 1100° C./2 hours: 68 m²/g    -   BET after 1100° C./20 hours: 56 m²/g

The composition of the composite material obtained according to Example13 corresponds exactly to the composition disclosed in example 24 of EP1 172 139. For the composition obtained according to example 24 of EP 1172 139, however, the following BET values are reported in EP 1 172 139:

-   -   BET after 1000° C./4 hours: 55 m²/g    -   BET after 1100° C./20 hours: 27 m²/g

From the above it is evident that the BET values of the compositionsurprisingly are much higher when prepared according to the process ofthe present invention than the BET values of the composition whenprepared according to prior art processes.

Example 14

CeO₂(24.1%) ZrO₂(17.3%) La₂O₃(0.5%) Y₂O₃(0.9%) Al₂O₃(57.2)

71.34 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.25%), 84.56 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%), 1.33 g of lanthanum nitrate in crystal form (La₂O₃content=37.7%) and 2.94 g of yttrium nitrate in crystal form (Y₂O₃content=38.2%) were treated with 300 mL of deionised water, the mixtureobtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 75.1 ml of cooled (10° C.) aqueous 35%H₂O₂ were added and the mixture obtained was stirred for approximately45 minutes. An aqueous 24% ammonia solution (cooled to 10° C.) was addeddropwise to the mixture with a dropping rate of 40 mL/minute until a pHvalue of 9.5 was adjusted. A precipitate formed and the aqueous slurry 1obtained was filtered. The solid obtained was washed with deionisedwater and was impregnated with 25.5 g Triton X-100®. The impregnatedsolid obtained was suspended in deionised water and the aqueous slurry 2obtained was mixed with 1271.11 g of Boehmite Suspension Type 1 (Al₂O₄content=4.5%). The aqueous suspension obtained was vigorously stirredusing an external stirrer for 2 hours and spray dried. The solidcomposition obtained was calcined at 850° C./4 hours. 100 g ofCeO₂(24.1%) ZrO₂(17.3%) La₂O₃(0.5%) Y₂O₃(0.9%) Al₂O₃(57.2) wereobtained.

-   -   BET after 850° C./4 hours (fresh material): 90 m²/g    -   BET after 1000° C./4 hours: 78 m²/g    -   BET after 1100° C./2 hours: 58 m²/g    -   BET after 1100° C./20 hours: 50 m²/g

The composition of the composite material obtained according to Example14 corresponds exactly to the composition disclosed in example 24 of EP1 172 139. For the composition obtained according to example 24 of EP 1172 139, however, the following BET values are reported in EP 1 172 139:

-   -   BET after 1000° C./4 hours: 55 m²/g    -   BET after 1100° C./20 hours: 27 m²/g

From the above it is evident that the BET values of the compositionssurprisingly are much higher when prepared according to the presentinvention than the BET values of the composition when prepared accordingto prior art.

Example 15

CeO₂(30%) ZrO₂(15%) La₂O₃(1.5%) Pr₆O₁₁(3.5%) Al₂O₃(50%)

61.86 g of an aqueous solution of zirconium nitrate (ZrO₂content=24.25%), 105.26 g of an aqueous solution of cerium nitrate (CeO₂content=28.5%), 3.98 g of lanthanum nitrate in crystal form (La₂O₃content=37.7%) and 8.97 g of praseodymium nitrate in crystal form(Pr₆O₁₁ content=39.02%) were treated with 460 mL of deionised water, themixture obtained was stirred for a few minutes and a clear solution wasobtained. To the mixture obtained 86.36 ml of cooled (10° C.) aqueous35% H₂O₂ were added and the mixture obtained was stirred forapproximately 45 minutes. To the mixture obtained an aqueous 24% ammoniasolution (cooled to 10° C.) was added dropwise with a dropping rate of40 mL/minute until a pH value of 9.5 was adjusted. The aqueous slurry 1obtained was filtered, the solid obtained was washed with deionisedwater and was impregnated with 28.54 g of Triton X-100® The impregnatedsolid obtained was suspended in deionised water to give aqueous slurry 2and was mixed with 1111.11 g of Boehmite Suspension Type 1 (Al₂O₃content=4.5%). The aqueous suspension obtained was vigorously stirredusing an external stirrer for 2 hours and filtered. The solid obtainedwas dried at 120° C. overnight and the solid composition obtained wascalcined at 850° C./4 hours. 100 g of CeO₂(30%) ZrO₂(15%) La₂O₃(1.5%)Pr₆O₁₁(3.5%) Al₂O₃(50%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 89 m²/g    -   BET after 1000° C./4 hours: 75 m²/g    -   BET after 1100° C./2 hours: 59 m²/g    -   BET after 1100° C./20 hours: 50 m²/g

Example 16

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) [Al₂O₃:La](50%)

137.36 g of Wet Cake B, obtained according to example A2 (ROI 18%) weresuspended in 150 mL of deionised water and stirred using an externalstirrer (Ultraturex) for 10 minutes. To the suspension obtained 16.4 gof Triton X-100® were added and the mixture obtained was stirred for 2hours. The suspension obtained was mixed with 629.72 g of La-dopedBoehmite Suspension Type 3 (Al₂O₃ content 3.97%). The slurry obtainedwas stirred for 2 hours at rt and filtered. The solid obtained was driedat 120° C. overnight and calcined at 850° C./4 hours. 50 g of CeO₂(10%)ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) [Al₂O₃:La](50%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 74 m²/g    -   BET after 1000° C./4 hours: 55 m²/g    -   BET after 1100° C./4 hours: 46 m²/g    -   BET after 1100° C./20 hours: 44 m²/g    -   BET after 1150° C./36 hours: 34 m²/g    -   BET after 1200° C./4 hours: 33 m²/g

Example 17

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) [Al₂O₃:La](50%)

137.36 g of Wet Cake B, obtained according to example A2 (ROI 18%) weresuspended in 150 mL of deionised water, the aqueous slurry 2 obtainedwas stirred using an external stirrer (Ultraturex) for 10 minutes andwas mixed with 629.72 g of La-doped Boehmite Suspension Type 3 (Al₂O₃content 3.97%). The aqueous suspension obtained was stirred for 2 hoursat rt and filtered. The solid obtained was dried at 120° C. overnightand the solid composition obtained was calcined at 850° C./4 hours.Approximately 50 g of CeO₂ (10%) ZrO₂ (36.5%) La₂O₃ (1%) Nd₂O₃(2.5%)[Al₂O₃:La](50%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 73 m²/g    -   BET after 1000° C./4 hours: 54 m²/g    -   BET after 1100° C./4 hours: 44 m²/g    -   BET after 1100° C./20 hours: 40 m²/g    -   BET after 1150° C./36 hours: 30 m²/g    -   BET after 1200° C./4 hours: 30 m²/g

Example 18

CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) [Al₂O₃:La](50%)

137.36 g of Wet Cake B, obtained according to example A2 (ROI 18%), weresuspended in 150 mL of deionised water, the mixture obtained was stirredusing an external stirrer (Ultraturex) for 10 minutes and 16.4 g ofTriton X-100® were added. The aqueous slurry 2 obtained was stirred for2 hours, mixed with 553.1 g of La-doped Boehmite Suspension Type 4(Al₂O₃ content 4.52%) and the aqueous suspension obtained was stirredfor 2 hours at rt and filtered. The solid obtained was dried at 120° C.overnight and the solid composition obtained was calcined at 850° C./4hours. Approximately 50 g of CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%)[Al₂O₃:La](50%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 90 m²/g    -   BET after 1000° C./4 hours: 67 m²/g    -   BET after 1100° C./4 hours: 49 m²/g    -   BET after 1100° C./20 hours: 45 m²/g    -   BET after 1150° C./36 hours: 35 m²/g    -   BET after 1200° C./4 hours: 30 m²/g

Example 19

CeO₂(10%), ZrO₂(36.5%) La₂O₃(1%) Nd₂O₃(2.5%) [Al₂O₃:La](50%)

137.36 g of Wet Cake B, obtained according to Example A2 (ROI 18%) weresuspended in 150 mL of deionised water and the aqueous slurry 2 obtainedwas stirred using an external stirrer (Ultraturex) for 10 minutes. Thesuspension obtained was mixed with 553.1 g of La-doped BoehmiteSuspension Type 4 (Al₂O₃ content 4.52%). The aqueous suspension obtainedwas stirred for 2 hours at rt and filtered. The solid obtained was driedat 120° C. overnight and the solid composition obtained was calcined at850° C./4 hours. Approximately 50 g of CeO₂(10%) ZrO₂(36.5%) La₂O₃(1%)Nd₂O₃(2.5%) [Al₂O₃:La](50%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 86 m²/g    -   BET after 1000° C./4 hours: 66 m²/g    -   BET after 1100° C./4 hours: 48 m²/g    -   BET after 1100° C./20 hours: 42 m²/g    -   BET after 1150° C./36 hours: 33 m²/g    -   BET after 1200° C./4 hours: 29 m²/g

Example 20

CeO₂(28.15%) ZrO₂(20.21%) La₂O₃(0.58%) Y₂O₃(1.05%) [Al₂O₃:La](50%)

110.62 g of Wet Cake C, obtained according to example A3 (ROI 18%) weresuspended in 150 mL of deionised water and the mixture obtained wasstirred using an external stirrer (Ultraturex) for 10 minutes. To thesuspension obtained 16.4 g of Triton X-100 were added and the mixtureobtained was stirred for 2 hours. The aqueous slurry 1 obtained wasmixed with 629.72 g of La-doped Boehmite Type 3 (Al₂O₃ content 3.97%).The aqueous suspension obtained was stirred for 2 hours at rt, filteredand the solid obtained was dried at 120° C. overnight. The solidcomposition obtained was calcined at 850° C./4 hours. Approximately 50 gof CeO₂(28.15%) ZrO₂(20.21%) La₂O₃(0.58%) Y₂O₃(1.05%) [Al₂O₃:La](50%)were obtained.

-   -   BET after 850° C./4 hours (fresh material): 73 m²/g    -   BET after 1000° C./4 hours: 68 m²/g    -   BET after 1100° C./4 hours: 48 m²/g    -   BET after 1100° C./20 hours: 44 m²/g    -   BET after 1150° C./36 hours: 36 m²/g    -   BET after 1200° C./4 hours: 35 m²/g

Example 21

CeO₂(28.15%) ZrO₂(20.21%) La₂O₃(0.58%) Y₂O₃(1.05%) [Al₂O₃:La](50%)

110.62 g of Wet Cake C, obtained according to example A3 (ROI 22.6%)were suspended in 150 mL of deionised water, the aqueous slurry 2obtained was stirred using an external stirrer (Ultraturex) for 10minutes and the suspension obtained was mixed with 629.72 g of La-dopedBoehmite Suspension Type 3 (Al₂O₃ content 3.97%). The aqueous suspensionobtained was stirred for 2 hours at rt, filtered, and the solid obtainedwas dried at 120° C. overnight. The solid composition obtained wascalcined at 850° C./4 hours. Approximately 50 g of CeO₂(28.15%)ZrO₂(20.21%) La₂O₃(0.58%) Y₂O₃(1.05%) [Al₂O₃:La](50%) were obtained.

-   -   BET after 850° C./4 hours (fresh material): 71 m²/g    -   BET after 1000° C./4 hours: 56 m²/g    -   BET after 1100° C./4 hours: 48 m²/g    -   BET after 1100° C./20 hours: 42 m²/g    -   BET after 1150° C./36 hours: 35 m²/g    -   BET after 1200° C./4 hours: 34 m²/g

Comparative Examples Comparative Example 1 CeO₂(10%) ZrO₂(36.5%)La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%) Preparation According to the ProcessDisclosed in Example 1 of EP 1 172 139

92.8 g of an aqueous solution of zirconium nitrate (ZrO₂ content=29.5%),26.32 g of an aqueous solution of cerium nitrate (CeO₂ content=28.5%),1.99 g of lanthanum nitrate in crystal form (La₂O₃ content=37.7%), 4.91g of neodymium nitrate in crystal form (Nd₂O₃ content=38.2%) and 275.74g of aluminium nitrate nonahydrate (Al₂O₃ content=13.6%) were treatedwith 600 mL of deionised water, the mixture obtained was stirred for afew minutes and a clear solution was obtained. To the mixture obtained4.62 mL of aqueous 35% H₂O₂ (1.2 molar ratio of cerium) were added andthe mixture obtained was stirred for approximately 20 minutes. To themixture obtained aqueous 24% ammonia solution was added in a shortperiod of time until a pH=7 was adjusted. The mixture obtained wasstirred for 15 minutes. The mixture obtained was filtered and theprecipitate obtained was washed with deionised water. The Wet Cake1_(COMP) obtained was dried at 120° C. and calcined at 300° C./5 hoursand afterwards burned at 700° C./5 hours. 75 g of CeO₂(10%) ZrO₂(36.5%)La₂O₃(1%) Nd₂O₃(2.5%) Al₂O₃(50%) were obtained.

-   -   BET after 300° C./5 hours+700° C./5 hours (fresh material): 148        m²/g    -   BET after 950° C./5 hours: 101 m²/g    -   BET after 1000° C./4 hours: 92 m²/g    -   BET after 1100° C./2 hours: 47 m²/g    -   BET after 1100° C./20 hours: 31 m²/g

Comparative Example 2 CeO₂(28%) ZrO₂(15%) Pr₆O₁₁(3.5%) Fe₂O₃(3.5%)[Al₂O₃:La](50%) Preparation According to Example 1 of U.S. Pat. No.5,883,037

The title composition corresponds to a composition of 50% Al₂O₃/La₂O₃(97%/3%) and 50% CeO₂/ZrO₂/Pr₆O₁₁/Fe₂O₃ (56%/30%/7%/7%). 78.33 g ofcerium acetate (CeO₂ content=47.9%), 90.13 g of zirconium acetate (ZrO₂content=22.3%), 9.79 g of praseodymium acetate (Pr₆O₁₁ content=47.9%)and 34.77 g ferric nitrate (Fe₂O₃ content=13.49%) were dissolved in 1350mL deionised water to yield a mixed metal solution. In a 4 L beakerapproximately 500 g of 24% ammonia were diluted to a total volume of2600 mL. Under vigorous stirring the mixed metal solution obtained wasadded to the ammonia solution obtained and a final pH of 10 was noted.To the mixture obtained 784.54 g of a slurry containing lanthanum dopedalumina (Al₂O₃ content=8.54%) were added under vigorous stirring and thevolume of the mixture obtained was raised to 4 L. The mixture obtainedwas filtered and the Wet Cake 2_(COMP) obtained was dried at 110° C. andcalcined at 600° C./2 hours. 134 g of CeO₂(28%) ZrO₂(15%) Pr6O₁₁(3.5%)Fe₂O₃(3.5%) [Al₂O₃:La](50%) were obtained. BET was measured at differentageing temperatures.

-   -   BET after 850° C./4 hours (Fresh material): 55 m²/g    -   BET after 1000° C./4 hours: 43 m²/g    -   BET after 1100° C./4 hours: 27 m²/g    -   BET after 1150° C./36 hours: 5 m²/g    -   BET after 1200° C./4 hours: 7 m²/g

Comparative Example 3 CeO₂(14.2%) ZrO₂(34.8%), Al₂O₃(51%) PreparationAccording to Example 6 of WO 2006/070201

To 112.5 g of aluminium nitrate nonahydrate (Al₂O₃ content=13.6%)dissolved in 1.5 L of deionised water 14.77 g of an aqueous solution ofcerium nitrate (CeO₂ content=28.85%) and 43.02 g of an aqueous solutionof zirconium nitrate (ZrO₂ content=24.27%) were added. The mixtureobtained was stirred for 15 minutes. To the mixture obtained a 25%aqueous solution of NaOH were added whereupon a precipitate formed. ThepH value was kept close to 10 during precipitation. To the slurryobtained 5 g of H₂O₂ were added and the pH of the mixture obtained wasadjusted to 10. The mixture obtained was stirred for 1 hour and the pHof the mixture obtained was adjusted to 8 using 30% nitric acid. Theslurry obtained was maintained at 60° C. for 1 hour. The mixtureobtained was filtered and the solid obtained was washed with deionizedwater at 60° C. until the electrical conductivity of the filtrate wasless than 0.5 S·m⁻¹. The Wet Cake 3_(COMP) obtained was isolated andresuspended in 850 mL of water, the pH of the slurry obtained wasadjusted to 10 and the mixture obtained was autoclaved at 120° C. for 6hours. The slurry obtained was cooled down and the pH of the mixtureobtained was adjusted to 8 using 30% nitric acid. The mixture obtainedwas stirred for 30 minutes. The slurry obtained was maintained at 60° C.for 1 hour and filtered. The solid obtained was washed with deionisedwater and directly calcined at 850° C. BET was measured at differentageing temperatures.

-   -   BET after 850° C./4 hours (Fresh material): 107 m²/g    -   BET after 1000° C./4 hours: 77 m²/g    -   BET after 1100° C./4 hours: 49 m²/g    -   BET after 1150° C./36 hours: 19 m²/g    -   BET after 1200° C./4 hours: 18 m²/g

The invention claimed is:
 1. A calcined mixed oxide comprising Al-, Ce-and Zr-oxides, wherein said mixed oxide comprises cerium from 5% to 80%by weight, aluminium from 40% to 70% by weight, zirconium from 5% to 80%by weight, and rare earth metals (RE) other than cerium from 0% to 12%by weight, wherein cerium, zirconium, aluminium and rare earth metals(RE) are calculated as CeO₂, ZrO₂, Al₂O₃, or RE₂O₃, respectively, andwherein said calcined mixed oxide is formulated so as to maintain asurface area (BET) exceeding 20 m²/g following calcination for 4 hoursat 1200° C.
 2. A calcined mixed oxide according to claim 1, wherein thecalcined mixed oxide is formulated so as to maintain a surface area(BET) exceeding 40 m²/g following calcination for 4 hours at 1200° C. 3.A calcined mixed oxide according to claim 1, wherein the calcined mixedoxide comprises: cerium from 5% to 40% by weight; zirconium from 5% to40% by weight, and rare earth metals (RE) other than cerium from 0.1% to9% by weight.
 4. A calcined mixed oxide according to claim 3, whereinthe calcined mixed oxide is formulated so as to maintain a surface area(BET) exceeding 40 m²/g following calcination for 4 hours at 1200° C.